The hormones released from the neuroendocrine bag cells of Aplysia induce egglaying and the associated behavior. This simple system provides a model in which to study peptide hormones that act at both the organ level and the neuronal level. We propose to isolate the hormones released by these cells and to determine their primary structure. Isolation and structural characterization is a prerequisite to detailed studies of the mechanism of action of these hormones. We have isolated the peptides from 900 Aplysia brasiliana and have fractionated this material on calibrated Sephadex columns. This study has revealed peptides of 24,400, 11,500, 8,100, 3,000, 2,300 and 1080 daltons. The peptides up to 8k daltons have now been purified by HPLC one major peptide in the 2K, 3K and 8K peaks and six peptides in the 1K peak. This summer we obtained 1,900 A. brasiliana and fractionation of this material is underway. The observation of major peak at 1K, 2K and 3K confirms our initial observations.